Fine-grained, completely decrystallized, annealed cobalt-iron-vanadium articles and method

ABSTRACT

Sheet or strip articles composed of an alloy nominally composed of about 49 percent cobalt, 49 percent iron and 2 per cent vanadium are disclosed which have a 0.2 per cent yield strength of about 70,000 p.s.i. or greater and a magnetic induction of about 20,000 gausses or greater at 13 oersteds and 22,400 gausses or greater at 85 oersteds are disclosed.

United States Patent [1 1 Fieldler Feb. 19, 1974 FlNE-GRAINED, COMPLETELY DECRYSTALLIZED, ANNEALED COBALT-lRON-VANADIUM ARTICLES AND METHOD [75] lnventor: Howard C. Fieldler, Schenectady,

[73] Assignee: General Electric Company,

Schenectady, N.Y.

22 Filed: Nov. 10,1972

[21] Appl. No.: 305,588

Related U.S. Application Data [63] Continuation of Ser. No. 847, Jan. 5, 1970,

abandoned.

[52] U.S. Cl 148/31.55, 148/120, 148/121 [51] Int. Cl C041) 35/00 [58] Field of Search 148/3l.55, 120, 121, 122; 75/123 K, 170, 134

[56] References Cited UNITED STATES PATENTS 3,622,409 11/1971 McCunn 148/122 3,597,286 8/1971 Thornburg 148/120 3,024,141 3/1962 Burket et al. 148/120 3,695,944 10/1972 Stroble 148/120 Binstock et al 148/122 1,862,559 6/1932 White et al.

3,065,118 11/1962 Wawrousek et al.

2,512,358 6/1950 McGeary 3,511,639 5/1970 3,657,026 4/1972 Coiling 148/120 OTHER PUBLICATIONS Barrett, C. et al.; Structure of Metals; New York,

1966 pp. 398-402 & 541-548 578-583 (TN 690B3) American Society for Metals, Metals Handbook, Cleveland, 1948, pp. 401-404 & Composite Page (TA472 A3) Primary ExaminerL. Dewayne Rutledge Assistant ExaminerW. R. Satterfield Attorney, Agent, or FirmJane M. Binkowski; Joseph T. Cohen; Jerome C. Squillaro [57] ABSTRACT 2 Claims, No Drawings 1 FlNE-GRA INED, COMILFTELY DECRYSTALLIZED, ANNEALED COBALT-lRON-VANADIUM ARTICLES AND METHOD These materials were obtained from the manufacturer as cold-rolled strip about 0.015 inch thick. Tensile test samples and magnetic test samples of these materials were given the conventional, so-called batch 5 heat treatments in the following manner. Samples were This is a continuation of copending application Ser. placed between thin alumina plates one-eighth inch or No. 847 filed Jan. 5, 1970 andnow abandoned, asone-fourth inch thick, sealed with foil in a metal retort signed to the assignee hereof.- through which dry hydrogen was circulated and heated This invention relates to magnetically soft alloys and in a hydrogen furnace which had been determined to more particularly to the treatment of an alloy of cobalt, be within 1C of the desired temperature. After a preiron and vanadium to produce optimum magnetic and determined time, the specimens were cooled in the furmechanical properties therein. nace at 50C per hour to 400C and the retort removed A commercially obtainable magnetically soft alloy of from the furnace and allowed to come to room tempercobalt, iron and vanadium, known as Vanadium Perature before opening. The 0.2 per cent strain yield mendur, is commonly used in sheet or strip form for IS strengths of these materials were then determined at a laminations for rotating electrical equipment such as Strain rate of 0.025 per minute, and the magnetic meaelectrical generators or motors, particularly where Sufemenls were made On One-fourth inch g Stacks Q weight is important. This material has a nominal comg mpl 1 inches and 1 inches or position of about 49 weight percent cobalt, 49 weight 1 inches and 2 O-D' Cut o t e specimens. percent iron and 2 weight percent vanadium, with small The following exemplary data iS g en f a 0. 2 amounts f various i i i h as lf b heat treated for times at temperature of 0.5 hour and oxygen and nitrogen. This material has both high maghours and are fairly yp of such materialsnetic saturation and zero magnetocrystalline anisotropy. While mechanical strength has not been of concern in the past, stresses produced by centrifugal force in newer, high speed generators, for example, may exceed the yield strength of conventional commercial Heat. No 2 Annealed 05 our matenal. Vanadium Permendur 1s conventionally sold Temperature, "C. as cold-rolled sheet or strip material, from which the a a a a purchaser may punch laminates, after which the 7 707 709 punched laminates are batch annealed to produce re- 0.2% vs. 109,520 91.070 72,080 57,990 crystal hzation and develop the desired magnetic prop 98mm 96,050 64.400 55,590 ert1es 1n the lamlnates. In the cold-rolled or mcom- 32,113 8,500 10,625 12,725 pletely recrystallized state, the mechanical properties B 85 21575 21-775 22,650 are high but the magnetic properties are low. After recrystallization, the mechanical properties are significantly lower but the magnetic properties are higher. It TABLE Ill would be desirable if such materials could be made with both high mechanical and magnetic properties and Heat No. 2 Annealed 2.0 Hours such is a principal object of this invention. Tempelaure' Briefly stated, and in accordance with one aspect of 01% 72,490 59mg J70 46.540 the invention, it has been found that Vanadium Per- 79.720 60.0w 5.320 46. 0 mendur may be treated so that the product has a con- 3:: 2 3:23? 33:32 trolled, small gram s1ze, substantially no gamma phase (an undesirable non-magnetic phase which may be present in conventionally produced material), which improved product has a high yield stress and high magnetic properties. More specifically, the material of the The above yield strengths are all longitudinal, i.e. the invention has a yield strength of about 70,000 p.s.i. or stress axis is parallel to the rolling direction. higher at 0.2 per cent strain, and a magnetic induction In all these, it will be seen that when the yield of not less than about 20,000 gausses at 13 oersteds and strength of the material is acceptably high, the mag- 22,40O gausses at 85 oersteds. netic inductance is not acceptably high, and when the In order to more clearly point out and describe the magneticproperties are acceptable, the yield strength invention, the following examples of mechanical and is too low. Upon metallographic examination of these magnetic properties achieved by the practice of the materials, it became evident that the better magnetic present invention upon Vanadium Permendur are COmproperties were exhibited by those samples which had pared to those properties conventionally exhibited by been completely recrystallized at higher temperatures this material. For this purpose, fourcommercial comand for the longer times at temperature. In those sampositions were employed. ples annealed, for example, at temperatures above TABLET Compositions (per cent by weight) Heat No, V Co Fe S C O N 702C for 2.0 hours, the completeness of recrystallization and grain growth lead to a sharp drop in yield Strength. An undesirable non-magnetic phase present as a precipitate was foundto be prevalent in samples annealed for 2.0 hours at 695 and 702C, visible in the 5 sample annealed at 710C and essentially absent from the sample annealed at 750C. In the samples annealed at the higher temperatures which produced essentially a single phase, the average grain size was large, for example, about A.S.T.M. 9 or less, or stated in terms of 10 grain size intercept length as about 12.5 microns or greater.

It was found that the desired combination of mechanical and magnetic properties in these materials could be achieved by treating the cold rolled material to produce a small recrystallized grain size by heating a short time to minimize grain growth and at a relatively high temperature to promote the nucleation of many rather than a few recrystallized grains, and at the same time,

TABLE IV Minutes within 10C Total Time Cycle of Max. Temp. (min.)

A 3.5 24 B 2 14 C 1 7 The following representative data for materials so heat treated on a traveling mesh belt through a metal retort which at one end was encased in a furnace and at the other by a water cooled jacket.

TKEIZE V Heat No. 2, Cycle A Maximum Temperature, C

0.2% Y.Sv 89,820 69,920 71,580 69,740 61,160

(p.s.i.)

B at 13 0e. 20,150 18,600 20,000 20,950

8 at 85 0e. 22,600 20,800 23,150 23,420

Heat No. 2, Cycle B Maximum Temperature, C

(p.s.i.)

' 80,910 78,300 73,370 70,410 63,700 B at 13 cc. 17,200 19,750 20,300 20,450 20,800 B at 85 cc. 22,750 22,450 22,650 22,625 22,725

Heat No. 3, Cycle B Maximum Temperature, C

(p.s.i.)

77,500 71,600 67,750 B at 13 cc. 20,075 20,450 B at 85 cc. 22,500 22,725

Heat No. 4, Cycle 13 Maximum Temperature, C

(p.s.i.)

B a! 13 cc. 19,750 20,225 20,500

B at 85 cc. 22,475 22,625 22,700

' Heat No. 1, Cycle B Maximum Temperature, C

(p.s.i.)

B at 13 ac. 19,125 20,650

B at 85 0e. 22,700

TABLE VI Tensile and Magnetic Properties, Cycle C. Heat No. 2 Maximum Temperature, C

(p.s.i.)

7 72,610 74,010 68,560 B at 13 cc. 20,075 20,300 20,300 B at 85 be. 22,575 22,600 22,500

TABLE VII Heat Treatment, Cycle C. Maximum Temperatures, 765C.

Heat No. 1 Heat No. 3 Heat No. 4

(p.s.i.)

78,430 71,950 71,650 B at 13 cc. 20,175 1 20,275 20,000 23,000 22,575 22,750

B at 85 oe.

growth. Based tpoabsservaiiani saafaesiasi'r'e.

crystallized materials should have an average grain size of less than about 8 microns, or, stated of ASTM grain size numbers, about 10.5 or greater. Such heat treatment may be readily achieved by a continuous strip anneal, by passing formed sheet or strip parts through a furnace on a belt or the like, or by using a salt bath, for example. When these materials are used as motor or generator laminations, they are conventionally punched or stamped from sheet or strip material having a thickness range of from about 4 mils to 25 mils, so such expedients as previously referred to are readily adapted to either the sheet or strip before or after the forming operation. 1

What I claim as new and desire to secure by Letters Patent of the United States is:

1. As an article of manufactureIa fulIy rea'ystallized body formed from a wrought sheet or strip consisting essentially of an alloy of about 49 percent cobalt, 49 percent iron and 2 percent vanadium, said body having a yield strength at 0.2 percent strain of about 70,000 psi or greater, a magnetic induction of at least about 20,000 gauss in a field of 13 oersteds and at least about 22,400 gauss in a field of oersteds, said body having an average grain size of about 8 microns or less and being characterized by the absence of the nonmagnetic gamma phase, said body having a completely recrystallized grain structure.

2. A method of processing an alloy consisting essentially of 49 percent iron, 49 percent cobalt and 2 per-,

cent vanadium, to develop an improved combination of magnetic properties and strength which comprises continuously annealing said alloy at a temperature from about 1367F to 1418F for a time sufficient to produce an average grain size of about 8 microns or less and a completely recrystallized grain structure and cooling to produce an annealed product which is characterized by the absence of the non-magnetic gamma phase and having a magnetic induction of at least 20,000 gauss in a field of 13 oersteds and at least about 22,400 gauss in a field of 85 oersteds and a yield strength of at least 70,000 psi. 

2. A method of processing an alloy consisting essentially of 49 percent iron, 49 percent cobalt and 2 percent vanadium, to develop an improved combination of magnetic properties and strength which comprises continuously annealing said alloy at a temperature from about 1367*F to 1418*F for a time sufficient to produce an average grain size of about 8 microns or less and a completely recrystallized grain structure and cooling to produce an annealed product which is characterized by the absence of the non-magnetic gamma phase and having a magnetic induction of at least 20,000 gauss in a field of 13 oersteds and at least about 22,400 gauss in a field of 85 oersteds and a yield strength of at least 70,000 psi. 